Variable optical attenuator

ABSTRACT

Two mirrors ( 15 ) and ( 16 ) making an angle of 90 degrees are formed on a front face of a mirror member ( 17 ). An optical fiber for input ( 12 ) and an optical fiber for output ( 13 ) are held in a fiber array ( 14 ) with a predetermined interval, and an emission lens ( 23 ) and an injection lens ( 24 ) are provided on a front face of the fiber array ( 14 ) in a way that they are opposed to end faces of the optical fiber for input ( 12 ) and the optical fiber for output ( 13 ) respectively. According to the variable optical attenuator, when the mirror member ( 17 ) is straightly moved by an actuator ( 18 ), light attenuation can be varied thereby.

TECHNICAL FIELD

The present invention relates to a variable optical attenuator that canadjust light attenuation.

BACKGROUND ART

The variable optical attenuator (VOA), which attenuates light injectedfrom an optical transmission channel for input (typically, opticalfiber) and outputs it to an optical transmission channel for output(typically, optical fiber), can variably adjust the light attenuation.As a method for controlling the light attenuation in such a variableoptical attenuator, various types have been proposed. For example, thereare a mechanical type in which a shutter is inserted/removed halfway anoptical path between opposed end faces of optical fibers and the lightattenuation is adjusted using a shading level by the shutter, and a typein which an optical element such as Faraday rotator or thermoopticelement is disposed halfway the optical channel.

However, in the first variable optical attenuator of the mechanicaltype, there is a problem of wavelength dependence orpolarization-dependant loss because of diffraction at an edge of theshutter. Furthermore, a conventional actuator used in themechanical-type attenuator is large in size, therefore miniaturizationof the variable optical attenuator has been difficult.

In the second variable optical attenuator using the optical element, thevariable optical attenuator is expensive because the expensive opticalelement such as Faraday rotator or thermooptic element is required, inaddition, since it does not have self-holding capability of the lightattenuation, current needs to be continuously applied to an electricalelement for affecting on the optical element, therefore powerconsumption has been large. Also, an electrical element for affecting onother optical elements or an optical element is necessary with regard tothe optical element, therefore a structure of the attenuator has beenapt to be complicated.

As a variable optical attenuator using a light reflection surface, anattenuator disclosed in U.S. Pat. No. 6,137,941 is known. FIG. 1 is aschematic view showing a structure of the conventional variable opticalattenuator. In the variable optical attenuator, as shown in FIG. 1, alens 3 is disposed on end faces of an optical transmission channel forinput 1 and an optical transmission channel for output 2 arrangedparallel, a mirror 4 is provided at a position distant from the lens 3only by the focal distance of the lens f, and the mirror 4 is rotatablysupported by a fulcrum 5. Here, an intermediate line between the opticaltransmission channel for input 1 and the optical transmission channelfor output 2 coincides with an optical axis of the lens 3, and thefulcrum 5 is located on an extension of the line. A piezoelectricactuator 7 is inserted between the mirror 4 and a base 6, and thepiezoelectric actuator 7 is expanded and contracted with beingcontrolled by a controller 8, thereby tilt of the mirror 4 can beoptionally adjusted.

Thus, when the mirror 4 is perpendicular to the optical axis of the lens3, light emitted parallel to the optical axis of the lens 3 from theoptical transmission channel for input 1 refracts when it transmitsthrough the lens 3 and then reaches the mirror 4, and the lightreflected on the mirror 4 refracts when it transmits through the lens 3and becomes parallel to the optical axis of the lens 3 and then it isinjected into the optical transmission channel for output 2. In thiscase, when an optical axis of the light injected into the opticaltransmission channel for output 2 coincides with an axis center of theoptical transmission channel for output 2, a quantity of light injectedinto the optical transmission channel for output 2 is maximized (thelight attenuation is minimized). On the contrary, when the mirror 4 istilted by the piezoelectric actuator 7, the optical axis of the lightthat is emitted from the optical transmission channel for input 1 andreflected on the mirror 4 and then returned to the optical transmissionchannel for output 2 is displaced from the axis center of the opticaltransmission channel for output 2, and the quantity of light injectedinto the optical transmission channel for output 2 decreases, thereforeas the tilt of the mirror 4 increases, the attenuation of the lightinjected into the optical transmission channel for output 2 increases.

According to the variable optical attenuator having such a structure,the problem such as the wavelength dependence in the variable opticalattenuator of the shutter type does not occur, in addition, the problemof high price due to the optical element can be avoided.

However, in the variable optical attenuator having such a structure, thelens 3 must be distant from the mirror 4 only by the focal distance ofthe lens 3, in addition, to reduce aberration of the light emitted fromthe optical transmission channel for input 1 or the light injected intothe optical transmission channel for output 2, a portion near theoptical axis of the lens 3 needs to be used as much as possible, and ashort-focus lens can not be used, therefore the miniaturization of thevariable optical attenuator has been restricted in such a structure. Inthe method of tilting the mirror 3, since the optical axis of lightinjected into the optical transmission channel for output 2 sensitivelydisplaces even upon slight tilt of the mirror 3, the tilt of the mirror3 needs to be controlled severely, therefore accurate control of thelight attenuation has been difficult. Since the piezoelectric actuatoris also used in this variable optical attenuator, the mirror 3 can nothold its angle by itself, resulting in large power consumption.

DISCLOSURE OF THE INVENTION

The invention, which was made in the light of such points, aims toprovide a variable optical attenuator that can be miniaturized and canaccurately control the light attenuation.

The variable optical attenuator according to the invention attenuatesthe light injected from the optical transmission channel for input andoutputs it into the transmission channel for output, and can adjust thelight attenuation, which has the optical transmission channel for input,the optical transmission channel for output, light reflection surfacesfor reflecting the light emitted from the optical transmission channelfor input to the optical transmission channel for output, and anactuator that straightly moves all or part of the light reflectionsurfaces relatively and straightly to at least one of the opticaltransmission channel for input and the optical transmission channel foroutput.

Here, in an embodiment of the variable optical attenuator according tothe invention, the actuator can straightly move one of at least part ofthe light reflection surfaces, the optical transmission channel forinput, or the optical transmission channel for output (hereinafter,referred to as light reflection surfaces and the like) such that theoptical axis of the light reflected to the optical transmission channelfor emission is displaced with respect to an axis center of the opticaltransmission channel for emission.

According to the variable optical attenuator according to the invention,the light reflection surfaces and the like for reflecting the lightemitted from the optical transmission channel for input is straightlymoved by the actuator, thereby the optical axis of the light injectedinto the optical transmission channel for output can be moved relativelyto the optical transmission channel for output, and thereby the lightattenuation can be varied. Here, while the light reflection surfaces canbe a surface capable of reflecting light, particularly, a mirror, mirrorsurface of metal, and mirror coating surface are desirable. Also, thelight reflection surface can be formed by a boundary surface oftransparent media having different refraction indicia (for example,boundary surface between a prism and air), wherein the light isperfectly reflected on the light reflection surfaces. The lightreflection surfaces can be not only surfaces formed to be a flatsurface, but also curved surfaces such as spherical surface. When any ofthe light reflection surfaces are the flat surfaces, a moving directionof the light reflection surfaces must not be parallel to surfacedirections of all the light reflection surfaces, however in case of thecurved surface, such restriction is eliminated. As the opticaltransmission channel for input or output, the optical fiber or anoptical waveguide channel can be used.

Thus, since the variable optical attenuator has a simple structure thatthe light reflection surfaces and the like for reflecting light emittedfrom the optical transmission channel for input are merely movedstraightly by the actuator, the variable optical attenuator can beminiaturized. In addition, because of only straightly moving the lightreflection surfaces and the like, the light attenuation does notsensitively respond upon variation during moving the light reflectionsurfaces compared with the attenuator using tilt of the light reflectionsurfaces, therefore the light attenuation can be accurately controlled.

Another embodiment of the variable optical attenuator according to theinvention has a monitor part which receives light that is emitted fromthe optical transmission channel for input but not injected into theoptical transmission channel for output. The variable optical attenuatorof the embodiment can indirectly know the quantity of light injectedinto the optical transmission channel for output, because it has themonitor part which receives the light that is not injected into theoptical transmission channel for output. In addition, since it does notdirectly detect the quantity of light injected into the opticaltransmission channel for output, loss of light outputted from thevariable optical attenuator is prevented. Also, monitoring accuracy canbe improved. Furthermore, by providing the monitor part in the variableoptical attenuator, an individual monitor need not be provided at, forexample, a subsequent stage of the variable optical attenuator,therefore entire cost including the monitor part can be reduced, inaddition, size is not substantially increased even if the monitor partis provided.

Furthermore, in the embodiment, an injection lens disposed oppositely tothe light injection surface of the optical transmission channel foroutput, and a monitor lens disposed oppositely to the light injectionsurface of the monitor part can be integrated. In such a variableoptical attenuator, since the injection lens and the monitor lens areintegrated, the quantity of light that is not injected into either theinjection lens or the monitor lens and causes loss can be decreased.Accordingly, the quantity of monitoring light increases and themonitoring accuracy can be improved. Furthermore, temperature rise inthe variable optical attenuator due to the light causing loss can beprevented.

Furthermore, in the embodiment, a function of correcting a position ofthe light reflection surfaces depending on output from the monitor partcan be provided. For example, the variable optical attenuator issubjected to feedback control using the monitor output outputted fromthe monitor part, thereby the attenuator can be controlled such that thequantity of light injected into the optical transmission channel foroutput is maintained to be constant, or the light attenuation isconstant.

In still another embodiment of the variable optical attenuator accordingto the invention, the actuator comprises a voice coil motor and a latchmechanism. In such a variable optical attenuator, since the voice coilis used, the actuator can be extremely diminished, in addition, theposition of the light reflection surfaces can be accurately adjusted.Furthermore, since the latch mechanism is provided, when the voice coilis not applied with current, the light reflection surfaces can be fixedby the latch mechanism. Particularly, by forming a non-electrical latchmechanism, power consumption can be reduced.

In still another embodiment of the variable optical attenuator accordingto the invention, a mirror member having the light reflection surfacesthat are two surfaces making an angle of 90 degrees, and the actuatorthat straightly moves the mirror member. According to such a variableoptical attenuator, since the two light reflection surfaces areintegrated into the mirror member such that they make the angle of 90degrees, alignment between the mirror member and the opticaltransmission channel for input as well as the optical transmissionchannel for output can be performed without needing adjusting an anglebetween the light reflection surfaces, therefore assemble of thevariable optical attenuator is facilitated.

Still another embodiment of the variable optical attenuator according tothe invention is characterized by having a fiber array that holds theoptical transmission channel for input and the optical transmissionchannel for output arranged parallel to each other. According to theembodiment, since the optical transmission channel for input and theoptical transmission channel for output are integrated into the fiberarray, alignment between the light reflection surface and the fiberarray can be performed without needing adjusting a positional relationbetween both the transmission channels, therefore assemble of thevariable optical attenuator is facilitated.

The components of the invention described above can be optionallycombined to the utmost extent.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic view showing a structure of a conventional,variable optical attenuator;

FIG. 2 is a plan view showing a structure of a variable opticalattenuator according to a first embodiment of the invention;

FIG. 3 is a perspective view of an actuator, a mirror member and a fiberarray forming the same, variable optical attenuator in a condition thatthey are separated with each together;

FIGS. 4 (1 a), (1 b) and (1 c) are schematic views for illustrating amethod for manufacturing the mirror member by metal pressing, and (2 a),(2 b) and (2 c) are schematic views for illustrating a method formanufacturing the mirror member by machining process;

FIG. 5 is a cross section view of the fiber array in a holder position;

FIGS. 6( a), (b) and (c) are views for illustrating operation and afunction of the variable optical attenuator shown in FIG. 2;

FIG. 7 is a view showing results of measuring a relation betweendisplacement between an optical axis of light injected into an injectionlens and an optical axis of the lens, and light attenuation;

FIG. 8 is an exploded schematic view showing a modification of thevariable optical attenuator shown in FIG. 2;

FIGS. 9( a), (b) and (c) are views for illustrating operation and afunction of the modification of the variable optical attenuator shown inFIG. 8;

FIG. 10 is a plan view showing a variable optical attenuator accordingto a second embodiment of the invention;

FIGS. 11( a), (b) and (c) are views for illustrating operation and afunction of the same variable optical attenuator;

FIG. 12 is a view showing relations between displacement between anoptical axis of light injected into an injection lens and an opticalaxis of the lens, and light attenuation in an optical fiber for outputas well as light attenuation in an optical fiber for monitor;

FIGS. 13( a) and (b) are views for illustrating difference between asingle-mode fiber and a multi-mode fiber;

FIG. 14 is a view for illustrating light which is not injected into boththe optical fiber for output and the optical fiber for monitoring andcauses loss;

FIG. 15 is a front view of a fiber array used in a variable opticalattenuator according to a third embodiment of the invention;

FIGS. 16( a) and (b) are a front view and a bottom view of a hybridlens, and (c) is a view showing the hybrid lens with being separatedinto an injection lens and a monitor lens;

FIG. 17 is a view showing an example of more detailed design of thehybrid lens;

FIGS. 18( a), (b), (c) and (d) are views for illustrating an aspect of adividing transition of collimated light by the hybrid lens;

FIG. 19 is a view for illustrating a conventional method of outputmonitoring;

FIG. 20 is a schematic block diagram showing a fourth embodiment of theinvention;

FIGS. 21( a) and (b) are views for illustrating a method for adjustinglight attenuation in the same variable attenuator incorporating acontrol circuit;

FIG. 22 is a flow diagram indicating a control operation of the variableattenuator incorporating the control circuit shown in FIG. 20;

FIG. 23 is a schematic block diagram showing a variable attenuatorincorporating a control circuit according to a fifth embodiment of theinvention;

FIG. 24 is a flow diagram showing control operation of the same variableattenuator incorporating the control circuit;

FIG. 25 is a schematic block diagram showing a variable attenuatorincorporating a control circuit according to a sixth embodiment of theinvention;

FIG. 26 is a view for illustrating the principles of constantattenuation control by the same variable attenuator incorporating thecontrol circuit;

FIG. 27 is a flow diagram showing control operation of the variableattenuator incorporating the control circuit shown in FIG. 25;

FIG. 28 is a view for illustrating a conventional method of constantattenuation control;

FIGS. 29( a) and (b) are schematic plan views showing a configuration ofa variable optical attenuator according to a seventh embodiment of theinvention;

FIGS. 30( a) and (b) are schematic plan views showing a differentconfiguration of the variable optical attenuator according to theseventh embodiment;

FIGS. 31( a), (b), (c) and (d) are schematic plan views showing aconfiguration and operation of a variable optical attenuator accordingto an eighth embodiment of the invention;

FIG. 32 is a perspective view of an actuator using a subminiaturevoice-coil-motor (VCM);

FIGS. 33( a) and (b) are side views for illustrating operation of alatch mechanism;

FIGS. 34( a), (b), (c) and (d) are schematic views for illustrating anactuator having another structure;

FIG. 35 is a view showing a part of an ultrasonic linear motor used asthe actuator in an expanded scale;

FIG. 36 is a plan view showing an actuator having still anotherstructure;

FIG. 37 is a plan view showing an actuator having still anotherstructure;

FIG. 38 is an exploded perspective view showing a latch mechanism havinganother structure;

FIGS. 39( a) is a side view of the same latch mechanism in a conditionthat a movable part is lowered, and (b) is a plan view thereof;

FIG. 40 is a side view of the latch mechanism of FIG. 38 in a conditionthat the movable part is raised;

FIGS. 41( a) is a side view showing a latch mechanism having a stillanother structure, and (b) is a plan view thereof;

FIG. 42 is a side view of the same latch mechanism in a condition that amovable part is lowered;

FIGS. 43( a) and (b) are side views showing a latch mechanism havingstill another mechanism;

FIGS. 44( a) and (b) are side views showing a latch mechanism havingstill another mechanism;

FIGS. 45( a) and (b) are side views showing a latch mechanism havingstill another mechanism;

FIG. 46 is a view showing an assembling procedure of a specific productof the variable optical attenuator;

FIG. 47 is a continuance view of FIG. 46;

FIG. 48 is a continuance view of FIG. 47;

FIG. 49 is a view indicating an example of a specific productconfiguration of the variable optical attenuator;

FIG. 50 is a view showing an example of a specific product configurationof the variable optical attenuator;

FIG. 51 is a view showing an example of a specific product configurationof the variable optical attenuator;

FIG. 52 is a view showing an example of a specific product configurationof the variable optical attenuator;

FIGS. 53( a) and (b) are schematic plan views showing a configuration ofa variable optical attenuator according to still another embodiment ofthe invention;

FIGS. 54( a), (b) and (c) are schematic plan views showing aconfiguration of a variable optical attenuator according to stillanother embodiment of the invention;

and FIGS. 55( a), (b) and (c) are schematic views for illustrating amethod for manufacturing the hybrid lens.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the best mode for carrying out the invention is describedin detail with reference to drawings.

First Embodiment

FIG. 2 is a plan view showing a structure of a variable opticalattenuator 11 according to the invention, and FIG. 3 is a perspectiveview of a member at a light reflection side of the attenuator and amember for light input/output in a condition that they are separatedfrom each other. The variable optical attenuator 11 comprises a fiberarray 14 having an optical fiber for input 12 (single-mode fiber) and anoptical fiber for output 13 (single-mode fiber); a mirror member 17having a first mirror 15 and a second mirror 16 intersecting at a rightangle of 90 degrees (both of them are assumed to have mirror surfacesmoothness of λ/10 or more); and an actuator 18 for straightly movingthe mirror member 17.

Two vertical mirrors 15, 16 which intersect at a right angle of 90degrees to each other in planar view are formed on the front of themirror member 17. The mirror member 17 comprises glass, siliconsubstrate, or metal such as brass, and the mirrors 15, 16 can be formedintegrally into the mirror member 17. Alternatively, the mirrors 15, 16that are members separated from the mirror member 17 can be pasted tothe mirror member 17.

For example, FIGS. 4 (1 a), (1 b) and (1 c) show a method formanufacturing the mirror member 17 by metal pressing. In FIG. 4 (1 a), asymbol 28 is a metal material plate, a symbol 29 a is a master forpressing, and a bottom of the master 29 a has a projection having anangle of 90 degrees. When the master 29 a is hit down and pressedagainst a top of the metal material plate 28, as shown in FIG. 4 (1 b),an orthogonal groove 30 having inner surfaces making an angle of 90degrees is formed on the upper surface of the metal material plate 28 bythe master 29 a. After the master 29 a is separated from the metalmaterial plate 28, when the metal material plate 28 is cut out along analternate long and short dash line shown in FIG. 4 (1 c), the mirrormember 17 is obtained. After that, surfaces in the orthogonal groove 30can be subjected to mirror polish.

FIG. 4 (2 a), (2 b) and (2 c) show a method for manufacturing the mirrormember 17 by machining process. A symbol 29 b shown in FIG. 4 (2 a) is acutter for machining, and both sides of the cutter 29 b make an angle of90 degrees at outer circumference of the cutter. When the upper surfaceof the metal material plate 28 is machined using the cutter 29 b, asshown in FIG. 4 (2 b), the orthogonal groove 30 having inner surfacesmaking an angle of 90 degrees is formed on the upper surface of themetal material plate 28 by the cutter 29 b. After that, when the metalmaterial plate 28 is cut out along an alternate long and short dash lineshown in FIG. 4 (2 c), the mirror member 17 is obtained. After that, thesurfaces in the orthogonal groove 30 can be subjected to the mirrorpolish.

Also, after forming the mirror member 17 having the orthogonal grooveusing the glass or silicon substrate, the mirrors 15, 16 can be formedby evaporating a metal thin film in the orthogonal groove.Alternatively, mirrors 15, 16 produced separately can be attached byadhesion in the orthogonal groove of the mirror member 17 made ofplastic. Also, the mirror member 17 can be formed by pasting a prismlens. Alternatively, after forming the mirror member 17 having theorthogonal groove using the glass or plastic, inner surfaces of theorthogonal groove, or an entire front face of the mirror member 17having the orthogonal groove can be subjected to the mirror coating.

Since a specific embodiment of the actuator 18 is described later, it issimply described here. The actuator 18 is a straight-moving-typeactuator comprising a stationary part 19 and a movable part 20, and themovable part 20 can reciprocate to the stationary part 19 in an arrowdirection in FIG. 2.

A fiber array 14 comprises a holder 21 that holds an optical fiber forinput 12 and an optical fiber for output 13, and a lens array 22 adheredon a front face of the holder 21. As shown in FIG. 5, the holder 21comprises a V groove array 25 a and a cover 25 b, and two V grooves 26are formed on an upper surface of the V groove array 25 a. A front endof the optical fiber for input 12 and a front end of the optical fiberfor output 13 are received in the V grooves 26, and the cover 25 b isintegrally adhered on top of them. Accordingly, in the holder 21, axiscenters of the optical fiber for input 12 and the optical fiber foroutput 13 are aligned at predetermined positions by the V grooves 26. Ona front face of the lens array 22 provided on the front face of theholder 21, small emission lens 23 (aspherical lens) and injection lens24 (aspherical lens) are formed. The lens array 22 is disposed on thefront face of the holder 21, and then light emitted from both theoptical fibers 12, 13 are emitted through both the lenses 23, 24,thereby both the optical fibers 12, 13 are aligned with both the lenses23, 24 by bringing optical axes of the fibers into line with those ofthe lenses, and then the array 22 is adhered and fixed on the front faceof the holder 21.

A lower surface of the mirror member 17 is fixed on the movable part 20of the actuator 18 by adhesive resin and the like, and the mirror member17 can move minutely in a lateral direction (method shown by arrows inFIG. 2) by driving the actuator 18. The fiber array 14 is disposed andfixed such that it is opposed to the front face of the mirror member 17,optical axes of the input optical fiber 12 and the emission lens 23 makean angle of 45 degrees to the mirror 15, and optical axes of the opticalfiber for output 13 and the injection lens 24 make an angle of 45degrees to the mirror 16. In a condition assembled in this way, an endface distance between the front face of the fiber array 14 and the frontend face of the mirror member 17 is 500 μm, and special optical pathlength from emission from the emission lens 23 to injection into theinjection lens 24 is 2 mm.

FIG. 6 is a view for illustrating operation and a function of thevariable optical attenuator 11. FIG. 6( a) indicates a condition where acenter of the mirror member 17 coincides with a center of the fiberarray 14, which are opposed to each other, wherein light emitted fromthe input optical fiber 12 is converted into collimated light (100 μm inbeam diameter) by the emission lens 23, the light 27 emitted from theemission lens 23 is reflected on the mirror 15, and further reflected onthe mirror 16, and then approximately all beams are injected into theinjection lens 24, and then light 27 condensed by the injection lens 24is injected into the output optical fiber 13 and then externallytransmitted. Accordingly, in this condition (condition of minimumdisplacement of the optical axis), the light attenuation is minimized.

FIG. 6( b) indicates a condition where the mirror member 17 is slightlymoved in a direction shown in an outline arrow (lateral direction) bythe actuator 18. In this condition, the light 27 emitted from theoptical fiber for input 12 is reflected on the mirrors 15, 16, and thenonly part of the light is injected into the optical fiber for output 13.Accordingly, in this condition, the light attenuation is large.

FIG. 6( c) indicates a condition where the mirror member 17 is movedonly a distance equal to a radius of the injection lens 24 in adirection shown in the outline arrow. In this condition, the light 27emitted from the optical fiber for input 12 is reflected on the mirrors15, 16, and then approximately all the light is irradiated outside theinjection lens 24, and hardly injected into the output optical fiber 13.Accordingly, in this condition, the light attenuation is maximized.

In the variable optical attenuator 11 of the invention, in a movablerange between FIG. 6( a) and FIG. 6( c), since the light attenuation canbe increased by moving the mirror member 17 to one of the lateraldirection (lower part in FIG. 6), and the light attenuation can bedecreased by moving the mirror member 17 to the other of the lateraldirection (upper part in FIG. 6), the mirror member 17 is moved by theactuator 18 and thus a stop position of the mirror member 17 isprecisely controlled, thereby the light attenuation can be preciselyadjusted. In a variable optical attenuator where distance between theoptical axes of the optical fiber for input 12 and the optical fiber foroutput 13 is 500 μm, interval between the front face of the fiber array14 and the front end face of the mirror member 17 is 500 μm, the beamdiameter of the collimated light is 100 μm, and tilt of the mirrors 15,16 with respect to the optical axis is 45 degrees, results of measuringa relation between the displacement between the optical axis of thelight injected into the injection lens 24 and the optical axis of theinjection lens 24, and the light attenuation are shown in FIG. 7. Whilethe light attenuation is indicated in negative values in FIG. 7, it isassumed that a large absolute value of the light attenuation implieslarge light attenuation. As found from the measurement results, anaspect that the light entering the optical fiber for output 13 isattenuated with increase of the optical-axis displacement can beconfirmed. The light attenuation with respect to the displacement of theoptical axis is determined according to conditions such as the beamdiameter, the optical path length, shapes of the lenses 23, 24, and thetilt of the mirrors 15, 16.

The variable optical attenuator of the invention is in a configurationwhere the light emitted from the optical fiber for input 12 is reflectedon the mirrors 15, 16, thereby the optical path of the light beaminjected into the optical fiber for output 13 is displaced by slidingthe mirror member 17 in an optical path system in which light is bent ata particular angle and emitted, and thereby the quantity of lightinjected into the optical fiber for output 13 is attenuated, thereforeit has following characteristics.

(1) A structure is simple, particularly the front end face of the mirrormember 17 and the front face of the fiber array 14 can be approachedwithout limit, unless they interfere with each other, therefore thevariable optical attenuator can be easily miniaturized.

(2) It is enough only if the mirror member 17 is slid straightly by theactuator 18. Since stroke control can be easily and accurately performedcompared with angle control, accuracy of moving distance of the mirrormember 17 or the displacement of the optical axis of the light injectedinto the optical fiber for output 13 is easily obtained, and the lightattenuation can be accurately controlled.

(3) The light attenuation can be varied in a continuous and steplessmanner.

(4) The diffraction as in the shutter-type variable-optical-attenuatordoes not occur, and the problems such as wavelength dependence areprevented.

(5) Since the expensive optical elements are not used, the actuator canbe manufactured at low cost.

FIG. 8 is an exploded perspective view showing a modification of theembodiment, and similarly as FIG. 3, the mirror member 17 and theactuator 18 are shown in a condition separated from the fiber array 14.In the variable optical attenuator 11, the mirror member 17 is formed bya triangle prism made of glass or plastic having a shape of an isoscelesright-angled triangle, and the mirrors 15 and 16 are formed byinterfaces between side faces intersecting at an angle of 90 degrees andair. On an incline (surface opposed to the optical fiber for input 12and the output optical fiber 13) 17 a of the triangle prism,antireflection (AR) coating comprising a dielectric multilayer film isdesirably applied.

Thus, even in the variable optical attenuator 11 of the modification,the mirror member 17 comprising the triangle prism is straightly movedby the actuator 18, thereby the light attenuation can be adjusted asshown in FIGS. 9( a), (b) and (c). That is, as shown in FIG. 9( a), in acondition where the center of the mirror member 17 coincides with thecenter of the fiber array 14, light 27 emitted from the optical fiberfor input 12 is converted into the collimated light (beam diameter of100 μm) by the emission lens 23, the light 27 injected into the mirrormember 17 is perfectly reflected on the mirror 15, and further perfectlyreflected on the mirror 16 and then emitted outside the mirror member17, and then approximately all beams are injected into the injectionlens 24, and then the light 27 condensed by the injection lens 24 isinjected into the optical fiber for output 13 and then externallytransmitted. It is a condition of minimum light attenuation.

As shown in FIG. 9( b), when the mirror member 17 is slightly moved in adirection of an outline arrow (lateral direction) by the actuator 18,light 27 emitted from the optical fiber for input 12 is injected intothe mirror member 17 and perfectly reflected twice by the mirrors 15, 16in the mirror member 17, and then only part of the light is injectedinto the optical fiber for output 13. It is a condition of intermediatelight attenuation.

As shown in FIG. 9( c), when the mirror member 17 is moved only thedistance equal to the radius of the injection lens 24 in a direction ofthe outline arrow, the light 27 emitted from the optical fiber for input12 is injected into the mirror member 17 and perfectly reflected twiceby the mirrors 15, 16 in the mirror member 17, and then approximatelyall the light is irradiated outside the injection lens 24. It is acondition of maximum light attenuation.

In this way, when the prism is used as the mirror member 17, since acommercially available prism can be used, price of parts can be reduced.

Although the actuator 18 is used to move the mirror member 17 withrespect to the fiber array 14 in this embodiment, it is allowable thatthe mirror member 17 is made stand still and the fiber array 14 is movedby the actuator 18 conversely.

Second Embodiment

FIG. 10 is a plan view showing a variable optical attenuator 31according to a second embodiment of the invention. The variable opticalattenuator 31 has a monitor output function. The fiber array 14 holdsthe optical fiber for input 12 and optical fiber for output 13comprising the single-mode fiber (10 μm in core diameter), and a opticalfiber 32 for monitoring comprising a multi-mode fiber (50 μm in corediameter), and the optical fiber for monitoring 32 is disposed near theoptical fiber for output 13. A monitor lens 33 is provided on the frontface of the lens array 22, and the monitor lens 33 is disposed at aposition adjacent to the injection lens 24. The monitor lens 33 and theoptical fiber for monitoring 32 are aligned such that their optical axescoincide with each other. Other configurations are same as the firstembodiment shown in FIG. 2, therefore description is omitted.

FIG. 11 is a view illustrating operation and a function of the variableoptical attenuator 31. FIG. 11( a) indicates a condition where thecenter of the mirror member 17 coincides with the middle between theinput optical fiber 12 and the output optical fiber 13, which areopposed to each other, wherein the light emitted from the input opticalfiber 12 is converted into the collimated light by the emission lens 23,the light 27 emitted from the emission lens 23 is reflected on themirror 15, and further reflected on the mirror 16, and thenapproximately all beams are injected into the injection lens 24, andthen the light 27 condensed by the injection lens 24 is injected intothe optical fiber for output 13. Accordingly, in this condition(condition of minimum light-axis displacement), the quantity of lightreceived by the optical fiber for output 13 is maximized. On the otherhand, since the light 27 is not injected into the monitor lens 33, thequantity of light received by the optical fiber for monitoring 32 isminimized.

FIG. 11( b) indicates a condition where the mirror member 17 is slightlymoved in a direction shown in an outline arrow (lateral direction) bythe actuator 18. In this condition, the light 27 emitted from theoptical fiber for input 12 is reflected on the mirrors 15, 16, and thenonly a part of the light is injected into the optical fiber for output13, and a part of the light 27 is injected into the optical fiber formonitoring 32. Accordingly, in this condition, the quantity of lightinjected into the optical fiber for output 13 is decreased, and thequantity of light injected into the optical fiber for monitoring 32 isincreased.

FIG. 11( c) indicates a condition where the mirror member 17 is movedonly a distance equal to the radius of the injection lens 24 in adirection of the outline arrow. In this condition, the light 27 emittedfrom the optical fiber for input 12 is reflected on the mirrors 15, 16,and then approximately all the light is irradiated on the monitor lens33, and hardly injected into the optical fiber for output 13. On theother hand, the quantity of light received by the optical fiber formonitoring 32 is maximized.

In the variable optical attenuator 31 of the invention, in a movingrange between a condition of FIG. 11( a) and a condition of FIG. 11( c),since the light attenuation can be increased by moving the mirror member17 to one of the lateral direction (lower part in FIG. 11), and thelight attenuation can be decreased by moving the mirror member 17 to theother of the lateral direction (upper part in FIG. 11), the mirrormember 17 is moved by the actuator 18 and a stop position of the mirrormember 17 is precisely controlled, thereby the light attenuation can beprecisely adjusted. In addition, since there is a certain relationbetween the quantity of light received by the optical fiber for output13 (or light attenuation) and the quantity of light received by theoptical fiber for monitoring 32, the quantity of light received by theoptical fiber for monitoring 32 is outputted as a monitor signal,thereby the light attenuation by the variable optical attenuator 31 canbe monitored, and accurate feedback can be performed. Accordingly, themonitor signal is fed back to the actuator 18, thereby accuracy ofadjusting the light attenuation can be improved.

FIG. 12 indicates a relation between the displacement between theoptical axis of the light injected into the injection lens 24 and theoptical axis of the injection lens 24, and the light attenuation in theoptical fiber for output 13 as well as the light attenuation in theoptical fiber for monitoring 32, which were measured under the sameconditions as in the case of FIG. 7. The light attenuation in theoptical fiber for monitoring 32 in FIG. 12 is light attenuationcalculated from the quantity of light received by the optical fiber formonitoring 32 using the maximum quantity of light received by theoptical fiber for output 13 as reference (therefore, the vertical axisof FIG. 12 can be considered as the quantity of received light on a logscale assuming that an upper part is a positive direction.) As seen fromthe measurement results, an aspect that the light entering the opticalfiber for output 13 is attenuated with increase of the displacement ofthe optical axis, at the same time, the quantity of light received bythe optical fiber for monitoring 32 increases can be confirmed, acertain relation exists between the light attenuation in the opticalfiber for output 13 and the quantity of light received by the opticalfiber for monitoring 32, and if the quantity of light received by theoptical fiber for monitoring 32 is known, light attenuation by thevariable optical attenuator 31 can be known.

The single-mode fiber is used for the optical fiber for input 12 and theoptical fiber for output 13, and the multi-mode fiber is used for theoptical fiber for monitoring 32, and the fiber array 14 is formed as amixed fiber array, which is intended to improve photosensitivity of themonitor. The single-mode fiber is typically used for an optical fiberfor communication, therefore the single-mode fiber is used for theoptical fiber for input 12 and the optical fiber for output 13. On theother hand, the multi-mode fiber can be used for the optical fiber formonitoring 32 without problems, because the fiber 32 is not used forcommunication, but used inside only for measuring the quantity of light.In addition, as shown in FIGS. 13( a) and (b), the multi-mode fiber(about 50 μm in core diameter) has a large diameter of a core 34compared with the single-mode fiber (about 10 μm in core diameter),therefore it has an advantage that it can condense a wider range oflight, and the multi-mode fiber that can improve the photosensitivity ofthe monitor is more effective in use for monitoring.

Although the multi-mode fiber is used for the optical fiber formonitoring 32 here, the single-mode fiber can be also used.

Third Embodiment

In the variable optical attenuator 31 according to the secondembodiment, when the optical axis of the light injected into theinjection lens 24 coincides with the optical axis of the injection lens24, approximately all the light is injected into the optical fiber foroutput 13, and when the optical axis of the light injected into themonitor lens 33 coincides with the optical axis of the monitor lens 33,approximately all the light is injected into the optical fiber formonitoring 32. However, when the optical axis of the light 27 injectedto the front face of the fiber array 14 does not coincide with both ofthe optical axis of the injection lens 24 and the optical axis of themonitor lens 33, as shown in FIG. 14, a part of the light 27 is injectedinto the optical fiber for output 13, and another part of the light isinjected into the optical fiber for monitoring 32, however, theremaining part (the shadowed area in FIG. 14) is not injected into theoptical fiber for monitoring 32 and deteriorates the monitoringsensitivity. In addition to the reduction in the monitoring sensitivity,a problem occurs: the light is irradiated on the front face of the fiberarray, thereby temperature of the fiber array 14 increases, as a resulttemperature of the variable optical attenuator 31 increases.

FIG. 15 is a front view of the fiber array 14 used in a variable opticalattenuator according to a third embodiment of the invention. Theembodiment, which is made in consideration with the problems, employs ahybrid lens 35 in which the injection lens and the monitor lens areunified. The hybrid lens 35 is formed by unifying an injection lens 24 aand a monitor lens 33 a having shapes shown in FIG. 16( c), and has afront pattern and a bottom pattern as shown in FIG. 16( a) and (b).First, the shape of the injection lens 24 a is described. An insideprofile circle 37 of the injection lens 24 a shown in FIG. 16( c)indicates a circle having a radius equal to a radius of a beam sectionof the collimated light (it is equal to an outline of the injection lens24 as shown in FIG. 14.) An outside profile circle 36 indicates anapproximately larger circle than the circle 37, which is an outerdiameter of the injection lens 24 a. A center of the circle 36 coincideswith a center of the circle 37, and an optical axis of the injectionlens 24 a also coincides with that center. The injection lens 24 a is ina shape that an area outside the circle 37 is removed over a range of180 degrees from a spherical or an aspherical lens having the circle 36as its outline. A profile circle 38 of the monitor lens 33 a shown inFIG. 16( c) can be a sufficiently large circle compared with the radiusof the beam section (exactly, it is a circle larger than a condensingrange for monitoring described later), and the monitor lens 33 a is in ashape that an area where the injection lens 24 a is overlapped isremoved from a spherical or an aspherical lens having the circle 38 asits outline. The hybrid lens 35 is formed in such a shape that part ofthe injection lens 24 a is fitted into the partially removed portion ofthe monitor lens 33 a. As shown in FIG. 16( b), the optical fiber foroutput 13 is disposed such that it coincides with an optical axis of theinjection lens 24 a, and the optical fiber for monitoring 32 is disposedsuch that it coincides with an optical axis of the monitor lens 33 a.

FIG. 17 shows an example of a further detailed design of the hybrid lens35. First, the circle 37 having the radius equal to the beam diameter ofthe light beam is drawn. Then, a circle 39 having the radius equal tothe beam diameter of the light beam is drawn such that it iscircumscribed with the circle 37. Next, a circle 41 is drawn, which iscircumscribed with the circle 39 and passes through an intersection of aperpendicular (straight line 40) passing through a center of the circle37 and a circle 37.

Furthermore, a large circle 36 concentric with the circle 37 is drawn,and one side area with respect to the straight line 40 outside thecircle 37 is removed, thereby a shape of the injection lens 24 a isdetermined. Also, a large circle 38 concentric with the circle 39 isdrawn, and an area overlapped with the injection lens 24 a is removedfrom the circle 38, thereby a shape of the monitor lens 33 a isdetermined. Then, a spherical or an aspherical lens having the opticalaxis at a center of the circle 36 is partially cut and thus the shape ofthe injection lens 24 a as above is formed. Also, a spherical or anaspherical lens having the optical axis at a center of the circle 38 ispartially cut and thus the shape of the monitor lens 33 a as above isformed. An area of removing an area of the circle 37 from an area withinthe circle 41 is a condensing area for monitoring 42, and assuming thata diameter of the collimated light is 100 μm, the condensing area formonitoring 42 is an area about 175 μm in diameter.

The hybrid lens 35 is produced integrally by using a technique forproducing the aspherical lens. Although the two lenses 24, 33 producedindividually can be pasted together, since optical loss occurs at abonded portion, integral molding is desirable.

FIGS. 18( a), (b), (c) and (d) are views for illustrating an aspect of adividing transition of the collimated light by the hybrid lens 35. Asshown in FIG. 18( a), when the light 27 is injected into the circle 37,approximately all the light 27 is injected into the injection lens 24 aand condensed by the injection lens 24 a, and then injected into theoptical fiber for output 13. On the other hand, when the light 27slightly moves to a monitor lens 33 a side, since an irradiated area bythe light 27 deviates from the circle 37, while the light 27 in thecircle 37 is condensed by the injection lens 24 and injected into theoptical fiber for output 13, the light 27 that deviates from the circle37 and enters a condensing area of monitoring 42 are wholly condensed bythe monitor lens 33 a, and then received by the optical fiber formonitoring 32. When the light 27 further moves greatly, and most of theirradiated area by the light 27 deviates from the circle 37, while smallquantity of the light 27 in the circle 37 is condensed by the injectionlens 24 and injected into the optical fiber for output 13, most of thelight 27 that deviates from the circle 37 and enters the condensing areafor monitoring 42 is condensed by the monitor lens 33 a and received bythe optical fiber for monitoring 32. Furthermore, when the areairradiated by the light 27 completely deviates from the circle 37,approximately all the light 27 is condensed by the monitor lens 33 a,and received by the optical fiber for monitoring 32.

In any of these conditions, it is found that the light that deviatesfrom the injection lens 24 a (for example, the light 27 shown in FIG.17) is wholly condensed by the monitor lens 33 a and received by themonitoring fiber 32, and used for the monitoring. Accordingly, the lightthat is not received by both of the injection lens 24 and the monitorlens 33 as shown in FIG. 14 disappears, and monitoring sensitivity andmonitoring accuracy are improved. Furthermore, it can be prevented thatthe light causes temperature rise in the variable optical attenuator 31.

As seen from the operation, while it is sufficient that the spherical oraspherical lens indicated by the circle 37 is used for the injectionlens 24 a, and a lens formed by removing the portion of the circle 37from the spherical or aspherical lens indicated by the circle 41 is usedfor the monitor lens 33 a, in the embodiment, the injection lens 24 a isformed large compared with the circle 37, and the monitor lens 33 a isalso formed large compared with an area of the condensing area formonitoring 42. This intends that feeble light that has deviated from thecircle 37 area or the condensing area for monitoring 42 is alsocondensed by the hybrid lens 35 and injected into the optical fiber foroutput 13 or the optical fiber for monitoring 32, thereby thetemperature rise in the fiber array 14 and the like is decreased as muchas possible.

The conventional, variable optical attenuator does not have themonitoring function. Therefore, as shown in FIG. 19, a splitter 44 thatbranches the light outputted from the variable optical attenuator 43 ina ratio of 99/1 is connected to a subsequent stage of the variableoptical attenuator 43, and 99% of the light is used as light output and1% of the light is used as the monitoring output. However, such aconfiguration has problems of output loss and bad monitoring accuracy. Acause of the former problem is that in such a method, output from thevariable optical attenuator 43 is divided into 99/1, therefore outputfrom the splitter 44 is 99% of the output from the variable opticalattenuator 43, or 1% of the output is necessarily lost. A cause of thelatter problem is that the quantity of the light outputted for themonitoring is only 1% of the output from the variable optical attenuator43, and the remaining 99% of the light must be calculated by using the1% of the light, therefore the monitor accuracy is bad, and correctingaccuracy of the quantity of the light output is bad even if the feedbackcontrol is performed.

On the contrary, in the second and third embodiments of the invention,since 100% of the output from the variable optical attenuator isoutputted to the subsequent stage, loss of the light output is small. Inaddition, since difference between the input and the output to and fromthe variable optical attenuator is the monitoring output, the quantityof monitoring light (absolute value) is large, and the light attenuationcan be accurately controlled. Particularly, in the third embodimentusing the hybrid lens 35, since the optical loss is hardly generated,further accurate control is possible.

Fourth Embodiment

FIG. 20 is a schematic block diagram showing a fourth embodiment of theinvention, and indicates a variable attenuator incorporating a controlcircuit 45. The variable attenuator incorporating the control circuit 45has the actuator 18, mirror member 17, and fiber array 14, which form avariable optical attenuator with the monitoring function as the thirdembodiment. The variable attenuator incorporating the control circuit 45further has a drive circuit 46 for driving the actuator 18, a controlcircuit 47 that controls the actuator 18 through the drive circuit 46and controls displacement of the optical axis of the collimated lightthat returns to the fiber array 14, a photo detector 48 such asphotodiode (PD) that receives the monitoring light outputted from theoptical fiber for monitoring 32 in the fiber array 14, and anamplification circuit 49 that amplifies an output signal from the photodetector 48 and inputs a feedback signal into the control circuit 47.The control circuit 47 communicates with a host system 50 throughcontrol voltage or a control signal.

Next, control operation for adjusting the light attenuation by thevariable attenuator incorporating the control circuit 45 is described.FIG. 22 is a flow diagram indicating the control operation. When thelight attenuation is adjusted or readjusted, first the control circuit47 outputs a control signal to the drive circuit 46 to drive theactuator 18, and as shown in FIG. 21( a), stops the mirror member 17 ata position where all the light that returns to the fiber array 14 isinjected into the monitor lens 33 (or at a position where the quantityof monitoring light is maximized while monitoring the monitoring lightreceived by the photo detector 48) (step S1). The quantity of lightreceived by the optical fiber for monitoring 32 at that time is assumedas the quantity of injected light I1 in light input and stored in amemory (step S2). Then, the light attenuation at which light output canbe maintained at a standard value 01 is calculated from the value of thequantity of injected light I1.

Next, the control circuit 47 outputs the control signal (controlvoltage) to the drive circuit 46 such that light attenuation becomes theoperated light attenuation (step S3), and returns the mirror member 17by the actuator 18 through the drive circuit 46 (step S4). As shown inFIG. 21( b), when the mirror member 17 stops at a position where thelight attenuation becomes the light attenuation calculated in this way,the quantity of light deviated from the optical fiber for output 13 andinjected into the optical fiber for monitoring 32 is measured by thephoto detector 48 (step S5), and a signal outputted from the photodetector 48 is amplified by the amplification circuit 49 and fed back tothe control circuit 47 as the monitoring signal. The control circuit 47calculates the quantity of monitoring light O2 from the monitoringsignal, and further calculates the quantity of light, O3=I1−O2, emittedfrom the optical fiber for output 13.

Whether the calculated value O3 of the quantity of injected light isequal to the standard value O1 is determined (step S6), and when it isnot equal, the control circuit 47 compares the quantity of injectedlight O3 calculated from the quantity of monitoring light O2 to thestandard value O1, and performs the feedback control on a position ofthe mirror member 17 such that the quantity of injected light approachesthe standard value O1, and corrects the quantity of injected light.

In a region of small displacement of the optical axis, since thequantity of light received by the optical fiber for monitoring 32 issmall, it is difficult to find a position where the displacement of theoptical axis is zero, or a position where the quantity of the lightreceived by the optical fiber for monitoring 32 is zero. In such a case,the position where the quantity of the monitoring light is zero can bepredicted based on change of the quantity of monitoring light before thequantity of light received by the optical fiber for monitoring 32approaches zero and based on previously stored data.

Fifth Embodiment

FIG. 23 is a schematic block diagram showing a fifth embodiment of theinvention, and indicates a variable attenuator incorporating a controlcircuit 145. The variable attenuator incorporating the control circuit145 has the actuator 18, mirror member 17, lens array 22, and fiberarray 14, which form the variable optical attenuator with the monitoringfunction as the third embodiment. The variable attenuator incorporatingthe control circuit 145 further has the drive circuit 46 for driving theactuator 18, and the control circuit 47 that controls the actuator 18through the drive circuit 46 and controls the displacement of theoptical axis of the collimated light that returns to the fiber array 14.The control circuit 47 communicates with the host system 50 through thecontrol voltage or the control signal. The variable attenuatorincorporating the control circuit 145 further has the photo detector 48such as photodiode (PD) that receives the monitoring light outputtedfrom the optical fiber for monitoring 32 in the fiber array 14; anoptical branch filter 147 that branches part of the light injected intothe fiber array 14 from the optical fiber for input 12 and extracts it;a photo detector 148 such as photodiode (PD) that receives the lightbranched in the optical branch filter 147; amplification circuits 49 and149 that amplify monitoring signals from the photo detectors 48, 148;and an arithmetic circuit 146. The optical branch filter 147 comprises ahalf mirror, splitter and the like.

Next, control operation for adjusting the light attenuation by thevariable attenuator incorporating the control circuit 145 is described.FIG. 24 is a flow diagram indicating the control operation. The opticalbranch filter 147 is assumed to branch the injected light to a fiberarray 14 side and a photo detector 148 side in a ratio of m to nrespectively. In this case, when the quantity of the injected lightinjected into the optical fiber for input 12 is assumed to be I4, thequantity of light I5 branched from the optical branch filter 147 to thephoto detector 148 is,I5=n·I4/(m+n);and the quantity of light I1 that is sent to the fiber array 14 side andemitted from the front end of the optical fiber for input 12 is,I1=m·I4/(m+n)=(m/n)I5.Therefore, in the variable attenuator incorporating the control circuit145, if part of the injected light injected from the optical fiber forinput 12 is branched to a photo detector 148 side by the optical branchfilter 147 (S11), and the quantity of the branched light 15 is measuredby the photo detector 148, the quantity of the injected light I1 of theinjected light injected into the mirror member 17 is obtained asI1=(m/n)I5 by the arithmetic circuit 146, and a value of the obtainedquantity of the injected light I1 is sent to the control circuit 47(S12).

Then, optical attenuation at which the light output can be maintained tothe standard value O1 is calculated from the value of the quantity ofthe injected light I1 by the control circuit 47. The control circuit 47outputs the control signal (control voltage) to the drive circuit 46such that light attenuation becomes the calculated light attenuation(step S13), and moves the mirror member 17 by the actuator 18 throughthe drive circuit 46 (step S14). When the mirror member 17 stops at aposition where light attenuation becomes the light attenuationcalculated in this manner, the quantity of the light O2 injected intothe optical fiber for monitoring 32 is measured by the photo detector 48(step S15), and the monitoring signal outputted from the photo detector48 is fed back to the arithmetic circuit 146. The arithmetic circuitcalculates the quantity of the injected light I1=(m/n)I5 from thequantity of the monitoring light I5 at an injection side, which isreceived from the photo detector 148, and calculates the quantity of theemitted light O3=I1−O2 by the optical fiber for output 13 from thequantity of the monitoring light O2 at an emission side, which isreceived from the photo detector 48.

Whether the calculated value O3 of the quantity of the emitted light isequal to the standard value O1 is determined (step S16), and when it isnot equal, the control circuit 47 compares the quantity of the emittedlight O3 calculated from the quantity of the monitoring light O2 to thestandard value O1, and performs the feedback control on the position ofthe mirror member 17 such that the quantity of the emitted lightapproaches the standard value O1, thereby corrects the quantity of theemitted light.

According to the embodiment, since the quantity of the injected light I1can be always monitored, the quantity of the injected light I1 can beobtained on real time even in the case that the quantity of the injectedlight varies, thereby the quantity of the emitted light can becontrolled such that it is exactly equal to the standard value O1.

Sixth Embodiment

FIG. 25 is a schematic block diagram showing a sixth embodiment of theinvention, and indicates a variable attenuator incorporating a controlcircuit 245 for realizing constant attenuation control. The variableattenuator incorporating the control circuit 245 also has the variableoptical attenuator with the monitoring function as the third embodiment,which comprises the actuator 18, mirror member 17, and fiber array 14.The variable attenuator incorporating the control circuit 245 furtherhas the drive circuit 46 for driving the actuator 18, the controlcircuit 47 that controls the actuator 18 and controls the displacementof the optical axis of the collimated light that returns to the fiberarray 14, the photo detector 48 that receives the monitoring lightoutputted from the optical fiber for monitoring 32 in the fiber array14, and the amplification circuit 49 that amplifies the output signalfrom the photo detector 48 and inputs the feedback signal into thecontrol circuit 47.

Next, control operation for maintaining the light attenuation to beconstant by the variable attenuator incorporating the control circuit 45is described. FIG. 26( a) and (b) are views for illustrating theprinciples for the constant attenuation control by the variableattenuator incorporating the control circuit 245 of the embodiment. Whenthe hybrid lens 35 as above is used, there is a relation of,quantity of injected light I1=[quantity of emitted light O3]+[quantityof monitoring light O2],among the quantity of the injected light I1 injected from the opticalfiber for input 12 to the mirror member 17, the quantity of the emittedlight O3 emitted into the optical fiber for output 13, and the quantityof the monitoring light O2 received by the optical fiber for monitoring32, therefore if the variable attenuator incorporating the controlcircuit 245 is controlled such that a value of the quantity ofmonitoring light 02 is constant,[quantity of injected light I1]−[quantity of emitted light O3]=constantvalue [quantity of monitoring light O2],is given. Accordingly, if the variable attenuator incorporating thecontrol circuit 245 as shown in FIG. 25 is controlled such that thequantity of the monitoring light O2 received by the photo detector 48 isconstant,quantity of emitted light O3=[quantity of injected light I1]−[constantattenuation],is given. That is, even if the quantity of the injected light varies aschange from a condition of FIG. 26( a) to a condition of FIG. 26( b),the quantity of the emitted light with attenuation that is constant atany time without regard to the variation of the quantity of the injectedlight can be outputted from the optical fiber for output 13.

FIG. 27 is a flow diagram illustrating a procedure for the constantattenuation control in the variable attenuator incorporating the controlcircuit 245 in FIG. 25. when the constant attenuation control isdescribed according to the flow diagram, first the control circuit 47 isinputted with a desired value of attenuation ΔD from the host system 50.When the desired value of attenuation ΔD is designated, the controlcircuit 47 stores the desired value as a desired value for the quantityof monitoring light O2 (step S21). Then, the current quantity ofmonitoring light O2 is measured by the photo detector 48 (step S22), anda signal outputted from the photo detector 48 is amplified by theamplification circuit 49 and fed back to the control circuit 47 as amonitoring signal. When the control circuit 47 knows the currentquantity of monitoring light O2, the circuit moves the mirror member 17by the actuator 18 through the drive circuit 46 such that the quantityof monitoring light O2 is equal to the desired value ΔD (step S23).

In this way, the mirror member 17 is controlled such that the quantityof monitoring light O2 is equal to the calculated desired value ΔD, andthen the quantity of monitoring light O2 injected into the optical fiberfor monitoring 32 is further measured (S24). Then, whether the measuredquantity of monitoring light O2 is equal to the desired value ΔD isdetermined (step S25), and if it is not equal, the control circuit 47compares the measured quantity of monitoring light O2 to the desiredvalue ΔD, and performs the feedback control on the position of themirror member 17 such that the quantity of monitoring light O2approaches the desired value ΔD, thereby corrects the quantity ofmonitoring light O2.

FIG. 28 is a view showing a conventional configuration for the constantattenuation control using the variable optical attenuator 43. In theconventional method, splitters 44 a, 44 b are connected before and afterthe variable optical attenuator 43 respectively, part of the lightinjected into the variable optical attenuator 43 is extracted from thesplitter 44 a and monitored by a photo detector 246, and part of thelight emitted from the variable optical attenuator 43 is extracted fromthe splitter 44 b and monitored by a photo detector 247. Then, thequantity of injected light injected into the variable optical attenuator43 is obtained from the quantity of monitoring light measured by thephoto detector 246, the quantity of the light emitted from the variableoptical attenuator 43 is obtained from the quantity of monitoring lightmeasured by the photo detector 247, and a difference value that thequantity of emitted light is subtracted from the quantity of injectedlight is compared to the desired value of attenuation ΔD, and when thedifference value between the quantity of injected light and the quantityof emitted light is not equal to the desired value of attenuation ΔD,the quantity of emitted light is subjected to the feedback control suchthat the difference between the quantity of injected light and thequantity of emitted light is equal to the desired value of attenuationΔD.

Therefore, similarly to the case described in the conventional exampleof FIG. 19, the conventional method has problems of loss of light outputand bad monitoring accuracy. According to the embodiment of theinvention described here, such problems can be solved.

Seventh Embodiment

FIG. 29 or FIG. 30 is a schematic plan view showing a configuration of avariable optical attenuation 51 according to a seventh embodiment of theinvention. In the variable optical attenuator 51, the mirror membercomprises a fixed mirror member 52 and a movable mirror member 53, onthe fixed mirror member 52, a mirror 54 inclined 45° with respect to theoptical axis of the light emitted from the optical fiber for input 12 isformed and on the movable mirror member 53, a mirror 55 inclined suchthat it makes an angle of 90 degrees with respect to the mirror 54 isformed. While the fixed mirror member 52 stands still with respect tothe fiber array 14, the movable mirror member 53 can straightly move ina direction parallel or perpendicular to the optical axis with respectto the fiber array 14 by the actuator.

FIGS. 29( a) and (b) show the movable mirror member 53 which is slid ina direction perpendicular to the optical axis of the fiber array 14.FIG. 29( a) indicates an aspect that the light 27 emitted from theoptical fiber for input 12 is converted into the collimated light by theemission lens 23, and then reflected on the mirror 54 and the mirror 55,and then all beams are condensed by the injection lens 24 and injectedinto the optical fiber for output 13. As shown by an outline arrow inFIG. 29( b), when the movable mirror member 53 is moved in a lateraldirection, the light 27 emitted from the optical fiber for input 12 isreflected on the mirrors 54, 55, and then only part of the light iscondensed by the injection lens 24 and injected into the optical fiberfor output 13. Accordingly, in this condition, the quantity of the lightinjected into the optical fiber for output 13 is decreased.

FIGS. 30( a) and (b) show the movable mirror member 53 which is slid ina direction parallel to the optical axis of the fiber array 14. FIG. 30(a) indicates an aspect that the light 27 emitted from the optical fiberfor input 12 is converted into the collimated light by the emission lens23, and then reflected on the mirror 54 and the mirror 55, and then allbeams are condensed by the injection lens 24 and injected into theoptical fiber for output 13. As shown by an outline arrow in FIG. 30(b), when the movable mirror member 53 is moved in a back and forthdirection, the light 27 emitted from the optical fiber for input 12 isreflected on the mirrors 54, 55, and then only part of the light iscondensed by the injection lens 24 and injected into the optical fiberfor output 13. Accordingly, again in this condition, the quantity of thelight injected into the optical fiber for output 13 is decreased.

As known from these embodiments, since the fixed mirror member only actsto bend a light direction, if the two optical fibers are held by thefiber array such that they make an angle of 90 degrees to each other, itis sufficient that only one mirror is provided (that is, the fixedmirror member can be omitted).

Eighth Embodiment

FIG. 31 is a schematic plan view showing a configuration of a variableoptical attenuator 62 according to an eighth embodiment of theinvention. The variable optical attenuator 62 comprises a fixed mirrormember 56 having two mirrors 57, 58 opposed in a valley-like patternwith making an angle of 90 degrees to each other, and a movable mirrormember 59 having two mirrors 60, 61 disposed in a mountain-like patternwith making an angle of 90 degrees to each other, and the movable mirrormember 59 straightly moves in and out from back of a valley portionbetween the mirrors 57 and 58.

Thus, when the movable mirror member 59 is retracted as FIG. 31( a), thelight 27 which is emitted from the optical fiber for input 12 andcollimated by the emission lens 23 is reflected on the mirrors 57 and58, and then wholly condensed by the injection lens 24 and injected intothe optical fiber for output 13. As shown in FIG. 31( b), when themovable mirror member 59 is slid by the actuator and slightly protrudedinto the optical cannel of the light 27, part of the light reflected bythe mirror 57 is shaded by the mirror 60, and the light 27 reflected onthe mirror 60 is condensed by the optical fiber for monitoring 32 andinjected into the optical fiber for monitoring 32. On the other hand,the quantity of light injected into the optical fiber for output 13 isdecreased. When the movable mirror member 59 is further protruded, thequantity of light injected into the optical fiber for output 13 isfurther decreased, and the quantity of light injected into the opticalfiber for monitoring 32 is further increased. When the movable mirrormember 59 is largely protruded by the actuator and the optical channelof the light 27 reflected on the mirror 57 is perfectly shaded, thelight 27 is not injected into the optical fiber for output 13, andapproximately all the light is injected into the optical fiber formonitoring 32.

Therefore, the variable optical attenuator with the monitoring functioncan be also realized by the variable optical attenuator 62 having such astructure.

Although the mirrors 60, 61 are formed on both sides of the movablemirror member 59 in the embodiment, the mirror 61 can be omitted. Thatis, a surface on which the mirror 61 is formed can not be always amirror, or an incline itself, on which the mirror 61 is formed, can notbe necessarily provided.

(Structure of Actuator)

Next, a specific configuration of the actuator 18, particularly anactuator having a self-holding function is described. FIG. 32 shows anactuator using a subminiature voice-coil-motor (VCM) 63. Magnets 65, 66are attached on upper and lower insides of a yoke 64 which is bent in atuning folk pattern respectively, and a magnetic field is generatedbetween the magnets 65 and 66. A voice coil 67 is formed by annularlywinding a coil and fastening it, one magnet 65 and the yoke 64 areinserted into the voice coil 67, and the voice coil 67 is moved smoothlyalong the magnet 65 by applying a weak force. Thus, when the voice coil67 is applied with electric current, the voice coil 67 moves in eitherdirection depending on a direction of the electric current due to theFleming's force generated in the voice coil 67. Therefore, if the voicecoil 67 is connected with the mirror member 17 using a certainconnecting member, the mirror member 17 can be straightly slid by thevoice coil motor 63.

Such a subminiature voice-coil-motor is used for an optical pickup, andproduced compactly and precisely utilizing a voice-coil-motor techniqueused for applications such as CD or MD. The voice coil motor iseffective as the actuator because of its compact size, excellentresponse, and fine feed (μm order) capability. However, the voice coilmotor is biased in an original direction by a return spring, and thrustis exerted for the displacement only while the electric current isapplied, therefore a latch mechanism is desirably added so that acondition can be maintained even if the electric current is cut off.

The latch mechanism can be formed by a typical magnetic circuit. Forexample, a latch mechanism 68 as shown in FIG. 33 (see FIG. 51 together)can be used. The latch mechanism 68 comprises a flat spring 69, coil 70,and magnet 71, and a rear anchor of the curved flat spring 69 is fixedto a holding part 74. An inside of a front end of the flat spring 69 isattached with the coil 70, and the coil 70 is opposed to the magnet 71.A movable part 72 is located below the front end of the flat spring 69,and the movable part 72 is pressed down at its front end by springstress of the flat spring 69. On the other hand, the holding part 74stood on an upper surface of a base 73 is fixed with one end of anelastic wire 75, and the other end of the wire 75 is connected with themovable part 72. Although the movable part 72 is biased by theelasticity of the wire 75 such that it rises from the base 73, thepressing force by the flat spring 69 is stronger than the biasing force.

Therefore, when the coil 70 is not applied with electric current, themovable part 72 is pressed against the base 73 by the front end of theflat spring 69 and fixed so that it does not move. When latch is desiredto be released, the coil 70 is applied with electric current to generateelectromagnetic attraction between the coil 70 and the magnet 71. Whenthe coil 70 is attracted to an upper part of the magnet 71 by theelectromagnetic attraction, the front end of the flat spring 69 israised, and the movable part 72 rises from the base 73, thereby themovable part 72 can be moved. Accordingly, the movable part 72 isconnected with the voice coil 67 of the voice coil motor 63, thereby thevoice coil 67 can be added with the latch mechanism.

If a silicone sheet is inserted between the flat spring 69 and themovable part 72 or between the movable part 72 and the base 73, or ifeach of contacting portions is formed from the silicone sheet, holdingforce by friction can be improved with shock being relaxed.

For the latch mechanism, in addition to this, any method such as methodusing a cam roller, method using oil pressure, and method using shapememory alloys can be used. The method can be preferably selected inconsideration of holding force, power consumption, a mounting space, andthe like.

(Structure of Another Actuator)

A type of the actuator is not limited as long as it is compact and canbe linearly driven. For example, a piezoelectric actuator using rapiddeformation of a piezoelectric element can be used. The actuator 76 isformed by connecting a moving object 77 and a weight part 79 via apiezoelectric element 78 as shown in FIG. 34. When the actuator 76 isretracted, the piezoelectric element 78 is slowly contracted as shown inFIGS. 34( a) to FIG. 34( b). Since the piezoelectric element 78 isslowly contracted, the moving object 77 does not move, remaining at restdue to friction between the object and a floor 80, and only the weightpart 79 moves backward. Then, the contraction of the piezoelectricelement 78 is suddenly stopped as FIG. 34( c), the actuator 76 as awhole moves backward due to inertia of the weight part 79 having largemass. Then, the piezoelectric element 78 is rapidly extended, since theweight part 79 having the large mass can not move due to the inertia,the moving object 77 is moved backward. Such actions as FIG. 34( a) to(d) are repeated many times, thereby the actuator 76 moves backward bysmall distances. Similarly, the actuator 76 can be moved forward. Inaddition, such an actuator 76 can be stood at an optional position whenthe piezoelectric element 78 is not driven, and can perform thesimilarly function as the latch mechanism.

(Structure of Still Another Actuator)

An ultrasonic linear motor 81 can be used as the actuator. FIG. 35 showsa part of the ultrasonic linear motor 81 in an enlarged scale. Theultrasonic linear motor 81 comprises a stator 82 comprising an elasticmaterial and a slider 83 contacting to a surface of the stator 82. Whenthe ultrasonic linear motor 81 is driven, surface grains of the stator82 perform an elliptical motion as shown in the figure, accordingly theRayleigh wave is transmitted over the surface of the stator 82, and theslider 83 is moved along the surface of the stator 82 due to frictionbetween the stator 82 and the slider 83. Accordingly, the slider 83 isbetter to be fixed with the mirror member 17. When the ultrasonic linearmotor 81 is not driven, since the slider 83 does not move due to thefriction between the stator 82 and the slider 83, the ultrasonic linearmotor 81 has the same function as the latch mechanism.

(Structure of Still Another Actuator)

A micro-stepping motor technique used for a miniature camera or aminiature movie camera can be used as the actuator. An actuator shown inFIG. 36 is formed by inserting a lead screw 85 provided on a rotationaxis of a stepping motor 84 into a nut (female screw hole; not shown)provided in the mirror member 17. If the mirror member 17 is set suchthat it does not rotate, the lead screw 85 is rotated by the steppingmotor 84, thereby the mirror member 17 can be moved along an axialdirection of the stepping motor 84.

An actuator shown in FIG. 37 is formed by engaging a worm gear 86mounted on a rotation axis of the stepping motor 84 with a lead screwwhich is disposed such that it intersects at right angle with therotation axis of the stepping motor 84 and pivoted by the axis.According to the actuator, the lead screw 85 is rotated by the steppingmotor 84 via the worm gear 86, thereby the mirror member 17 can be movedin a direction perpendicular to the axial direction of the steppingmotor 84.

(Structure of Another Latch Mechanism)

Next, another embodiment of the latch mechanism 68 is described, whichis provided for that even if power of the actuator is turned off aftermoving the mirror member 17 by the actuator such as voice coil motor,the mirror member 17 is held a at that position.

FIG. 38 is an exploded perspective view showing another latch mechanism68, FIGS. 39( a) and (b) are a side view and a plan view when themovable part is lowered, and FIG. 40 is a side view when the movablepart is raised. In the latch mechanism 68, a drive part 112 is arrangedat a center of an upper surface of a substrate 111. In the drive part112, an armature 114 is rotatably supported by an axis 115 at an upperpart in a casing 113, and the armature 114 is exposed from an uppersurface of the casing 113. On an upper surface of one end of thearmature 114, a projection 116 is provided. The drive 112 can rotate thearmature 114 using an electric signal to switch an inclined direction ofthe armature 114.

In the drive part 112, the armature 114 is inclined such that theprojection 116 protrudes upward during power-on, and inclined such thatthe projection 116 retracts downward during power-off. Alternatively,the drive part 112 can be a self-holding type, and in this case, whilepower is necessary when the armature 114 is moved, after the armature114 is moved to a predetermined angle, the armature 114 is held byitself and fixed as it is even if the power is turned off. As such aself-holding-type drive part 112, a mechanism used for driving a contactspring in, for example, a self-holding-type electromagnetic relay(latching relay) can be used, wherein an electromagnet that is excitedby current application to move the armature, and a latch mechanism forlocking the armature to its angle when current is not applied areinternally incorporated. However, in the following description, it isassumed that the drive part 112 is not the self-holding type.

A spring support part 117 is vertically arranged on the upper surface ofthe substrate 111 at a rear of the drive part 112, and rear anchors of aplurality of linear springs 118 are fixed to both side portions of afront face of the spring support part 117 respectively. A movable part119 is disposed at a front of the drive part 112, and the movable part119 is connected with front ends of the plurality of linear springs 118and elastically supported by the linear springs 118. When the movablepart 119 is not applied with external force, the part is maintained at apredetermined height above the substrate 111 due to elasticity of thelinear springs 118. The mirror member 17 is fixed on a front of themovable part 119.

The drive part 112 can be moved laterally using the actuator such asvoice coil motor in the condition that it is supported above thesubstrate 111 by the linear springs 118. Stoppers 120 protrude from bothside portions of the movable part 119 toward both side faces of thedrive part 112; and the stoppers 120 contact to the drive part 112,thereby a range of lateral movement of the movable part 119 isrestricted.

An elastic member 121 is fixed on an upper surface of the spring supportpart 117. The elastic member 121 is formed into an approximately Tpattern using a flat spring, and a portion of its rear anchor having alarge width is fixed to the upper surface of the spring support part117. A projection 122 is provided on a lower surface at a front end ofthe elastic member 121, and the front end of the elastic member 121 andthe projection 122 are opposed to an upper surface of the movable part119. The projection 116 provided on the front end of the armature 114 isopposed to a lower surface of a front portion of the elastic member 121.The force that the elastic member 121 presses down the movable part 119is larger than the force that the linear springs 118 raises the movablepart 119, and in a condition that the elastic member 121 is not appliedwith force from the armature 114, the elastic member 121 presses downthe movable part 119 using the projection 122, and presses the movablepart 119 against the substrate 111 and locks the part so that it can notmove.

Thus, as shown in FIG. 39( a), when the movable part 112 is in apower-off state and the armature 114 is lowered at a side provided withthe projection 116, the movable part 119 is pressed down by the elasticmember 121, and pressed against the substrate 111 and thus locked.

On the other hand, as shown in FIG. 40, when power of the drive part 112is turned on to drive the armature 114, and the side provided with theprojection 116 is protruded upward, the elastic member 121 is raised bythe projection 116 and thus curved, the projection 122 on the elasticmember 121 is separated from the movable part 119, and the movable part119 is raised from the substrate 111 by elastic force of the linearsprings 118. In this condition, since the movable part 119 can be movedlaterally by the actuator, the movable part 119 attached with the mirrormember 17 is moved by the actuator, thereby the light attenuation can befreely adjusted.

After the light attenuation is adjusted to a desired value, when thepower of the drive part 112 is turned off, the armature turns aroundagain, and the projection 116 is lowered. As a result, the movable part119 is pressed down by the elastic force of the elastic member 121 andpressed against the substrate 111, and thus locked again. Accordingly,if such a latch mechanism 68 is used, it is enough that the drive part112 is applied with electric current only when the mirror member 17 ismoved by the actuator, the drive part 112 needs not be applied withelectric current after the position of the mirror member 17 is adjustedand thus the movable part 119 is locked, and as a result power saving ofthe latch mechanism 68 can be achieved.

(Structure of Still Another Latch Mechanism)

FIGS. 41( a) and (b) are a side view and a plan view of a still anotherlatch mechanism 68 when the movable part 119 is raised, and FIG. 40 is aside view of the mechanism when the movable part 119 is lowered.Although the latch mechanism 68 according to the embodiment has anapproximately similar structure as in the embodiment shown in FIG. 38,structures of the armatures 114 and the elastic member 121 are differentfrom those in FIG. 38. In the embodiment, a pair of posts 123 is stoodon both side edges of the substrate 111, and both ends of a rotationalaxis 124 fixed to a lower surface at a center of the elastic member 121are rotatably supported by the posts 123. Accordingly, the elasticmember 121 rotates about the rotational axis 124. The projection 116 isprovided on a rear end of the armature 114 exposed from the uppersurface of the drive part 112, and the projection 116 is opposed to thelower surface at the rear (backside from the rotational axis) of theelastic member 121. In the drive part 112, the armature 114 is inclinedsuch that the projection 116 protrudes upward during power-off, andinclined such that the projection 116 is retracted downward duringpower-on.

Thus, when the drive part 112 is in the power-off state, as shown inFIG. 42, since the armature 114 is inclined and its rear provided withthe projection 116 is protruded upward, a rear of the elastic member 121is pressed upward by the projection 116, and the projection 122 providedon a front of the elastic member 121 elastically presses down themovable part 119 as a reaction. As a result, the movable part 119 ispressed against the substrate 111, and locked so that it can not movelaterally.

On the contrary, when the movable part 112 is in the power-on state, asshown in FIG. 41( a), since the armature 114 is turned around and itsrear provided with the projection 116 is lowered and removed from theelastic member 121, the movable part 119 attached with the mirror member17 is raised by the linear springs 118 and thus can be moved laterallyby the actuator.

In this way, the movable part 119 is moved by the actuator, thereby theposition of the mirror member 17 is adjusted. After that, when the powerof the drive part 112 is turned off again, the projection 116 is raisedupward and pressed up the rear of the elastic member 121, and themovable part 119 is pressed against the substrate 111. Accordingly, themovable part 119 is locked so that it does not move in a condition thatthe position of the mirror member 17 is adjusted.

(Structure of Still Another Latch Mechanism)

FIGS. 43( a) and (b) are side views for illustrating a structure andoperation of still another latch mechanism 68. In the embodiment, asdescribed below, the armature 114 of the drive part 112 is formed froman elastic material such as flat spring, thereby the armature 114 has afunction as an elastic member. In the drive part 112 used in theembodiment, the front of the armature 114 is extended externally to thecasing 113, in addition, the front of the armature 114 is bent stepwisesuch that the armature 114 is not hit with the casing 113 when thearmature 114 is rotated. Then, the projection 116 is provided on thelower surface at the front end of the armature 114, and the projection116 is opposed to the upper surface of the movable part 119. In thedrive part 112, the front provided with the projection 116 is loweredduring power-off, and the armature 114 rotates and the front providedwith the projection 116 is raised upward during power-on.

Thus, when the drive part 112 is in the power-off state, as shown inFIG. 43( b), the front of the armature 114 provided with the projection116 is lowered, and the movable part 119 is pressed against thesubstrate 111 by the projection 116 and locked. On the contrary, whenthe power of the drive part 112 is turned on, as shown in FIG. 43( a),the armature 114 is inclined and the front provided with the projection116 rises above the upper surface of the movable part 119, and themovable part 119 is raised by the linear springs 118. In this condition,the movable part 119 is moved laterally by the actuator, thereby thelight attenuation can be adjusted by the mirror member 17. After it hasbeen adjusted, when the power of the drive part 112 is turned off, thecondition in FIG. 43( b) is returned, and the movable part 119 adjustedis locked.

(Structure of Still Another Latch Mechanism)

FIGS. 44( a) and (b) are side views for illustrating a structure andoperation of a still another latch mechanism 68. In the latch mechanism68 according to the embodiment, a piezoelectric actuator 125 is usedinstead of using the movable part. That is, in the embodiment, a pair ofposts 123 are stood on both side edges of the substrate 111, and bothends of the rotational axis 124 fixed to the lower surface at the centerof the elastic member 121 are rotatably supported by the posts 123. Theprojection 122 provided on the lower surface at the front end of theelastic member 121 is opposed to the upper surface of the movable part119 supported by the linear springs 118. On the upper surface at therear of the substrate 111, a piezoelectric actuator 125 that verticallyexpands and contracts is stood; and the lower surface at the rear of theelastic member 121 is bonded to the upper surface of the piezoelectricactuator 125.

Thus, in a condition that the piezoelectric actuator 125 is not appliedwith voltage, as shown in FIG. 44( a), the rear of the elastic member121 is pressed up, and the front of the elastic member 121 is rotateddownward due to the principles of the lever, thereby the projection 122is elastically pressed against the upper surface of the movable part119. As a result, the movable part 119 is lowered and pressed againstthe substrate 111 and thus locked. On the contrary, when thepiezoelectric actuator 125 is applied with voltage and thus thepiezoelectric actuator 125 is contracted, as shown in FIG. 44( b), therear of the elastic member 121 is pulled down, and the front of theelastic member 121 is raised upward due to the principles of the lever,thereby the projection 122 is separated from the upper surface of themovable part 119. As a result, the movable part 119 is raised upward bythe linear springs 118, and the movable part 119 is moved laterally,thereby the light attenuation can be adjusted by the mirror member 17.

(Structure of Still Another Latch Mechanism)

FIGS. 45( a) and (b) are side views for illustrating a structure andoperation of a still another latch mechanism 68. In the latch mechanism68 according to the embodiment, an electromagnet 127 is used instead ofusing the movable part. That is, again in the embodiment, a pair ofposts 123 are stood on both side edges of the substrate 111, and bothends of the rotational axis 124 fixed to the lower surface at the centerof the elastic member 121 are rotatably supported by the posts 123. Theprojection 122 provided on the lower surface at the front end of theelastic member 121 is opposed to the upper surface of the movable part119, and the lower surface at the rear end of the elastic member 121 isbound with a magnetic adsorption strip 126 such as iron strip. Anelectromagnet (electromagnetic coil) is stood on the upper surface atthe rear of the substrate 111; and the magnetic adsorption strip 126provided on the lower surface at the rear of the elastic member 121 isopposed to the electromagnet 127. Compression springs 128 are stretchedbetween the lower surface at the front of the elastic member 121 and theupper surface of the substrate 111, and the front of the elastic member121 is biased by the compression springs 128 such that it is pulleddownward.

Thus, as shown in FIG. 45( a), when the electromagnet 127 isdemagnetized, since the front of the elastic member 121 is pulleddownward by the elastic force of the compression spring 128, theprojection 122 is pressed against the upper surface of the movable part119. As a result, the movable part 119 is lowered and pressed againstthe substrate 111 and thus locked. On the contrary, as shown in FIG. 45(b), when the electromagnet 127 is excited, since the magnetic adsorptionstrip 126 provided on the rear end face of the elastic member 121 isadsorbed by the electromagnet 127 against the elastic force of thecompression spring 128, the front of the elastic member 121 is raisedupward due to the principles of the lever, thereby the projection 122 isseparated from the upper surface of the movable part 119. As a result,the movable part 119 is raised upward by the linear springs 118.Accordingly, the movable part 119 is moved laterally by the actuator,thereby the light attenuation can be adjusted by the mirror member 17.

(Specific Products)

FIG. 46 to FIG. 48 show an assembling procedure of a specific product ofthe variable optical attenuator. In the assembling, a fiber-arrayholding part 88, the actuator 18, and a latch mechanism 89 as requiredhave been previously mounted. Then, as shown in FIG. 46, the mirrormember 17 is attached and fixed to the actuator 18. Then, as shown inFIG. 47, a fiber array 14 is mounted in the fiber-array holding part 88,and aligned while light is emitted from the optical fiber for input 12,and after a position of the fiber array 14 is determined, the fiberarray 14 is fixed to the fiber-array holding part 88. Then, as shown inFIG. 48, the substrate 98 mounted with the fiber array 14, mirror member17, and actuator 18 is contained in a package 90.

FIG. 49 indicates an example of a specific product configuration. It isan example of a configuration without the control circuit. The actuator18 is fixed in the package 90, and the mirror member 17 is attached tothe actuator 18. The fiber array 14 is mounted in the fiber-arrayholding part 88, opposing to the mirror member 17. Optical fibers 91(such as the optical fiber for input 12 and the optical fiber for output13) in the fiber array 14 are led out externally to the package 90through a connector 92 and a cover 93. The drive circuit 46 of theactuator 18 is also contained in the package 90.

FIG. 50 is an example of a specific configuration with the controlcircuit. In the example, in addition to the components in FIG. 49, thephoto detector for monitoring 48, amplification circuit 49, and controlcircuit 47 are contained in the package 90.

FIG. 51 shows a more specified configuration of the configuration inFIG. 49. That is, the voice coil motor 94 is used as the actuator 18.That is, the voice coil 96 is opposed to the magnet 95 fixed to the base87, and the voice coil 96 is fixed to the movable part 72. The mirrormember 17 is also fixed to the movable part 72. While the latchmechanism 68 having a structure as shown in FIG. 33 is used as the latchmechanism, only the holding part 74, wire 75, and movable part 72 areshown in FIG. 51, and the flat spring 69, coil 70, and magnet 71 areomitted. The wire 75 the rear anchor of which is held by the holdingpart 74 has elasticity, and raise the movable part 72 attached to itsfront end upward. The movable part 72 is slidable along the wire 75.

Thus, when the mirror member 17 is latched so that it does not move, theflat spring 69 presses the movable part 72 against the base 87. In thecase that the mirror member 17 is moved, when the coil 70 is excited toraise the front end of the flat spring 69 (see FIG. 33), the movablepart 72 is raised from the base 87 by the wire 75, and the voice coil 96is opposed to the magnet 95. Then, when the voice coil 96 is excited,the voice coil 96 slides together with the movable part 72, and theposition of the mirror member 17 is adjusted.

FIG. 52 also shows a more specified configuration of the configurationin FIG. 49, which employs the actuator having a structure as in FIG. 37that comprises the stepping motor 84, lead screw 85, and worm gear 86.However, the lead screw 85 is rotated via the worm gear 86, thereby thestage 99 is moved along the lead screw 85, and the mirror member 17 isfixed on the stage 99. In addition, the guide pin 97 is inserted intothe stage 99, thereby the stage 99 is guided and can be smoothly moved.

Next, a special use of the variable optical attenuator is described.FIG. 53 shows a variable optical attenuator 100 that can be used as anon/off switch by making the light attenuation by the attenuator to bebinary, that is, 0% and 100%. While the variable optical attenuator 100has the same structure as the variable optical attenuator 11 accordingto the first embodiment shown in FIG. 3 and the like, the mirror member17 quickly moves by the actuator 18 between a condition where all thebeams are injected into the injection lens 24 as shown in FIG. 53( a)and a condition where all the beams deviates from the injection lens 24as shown in FIG. 53( b), and it does not stop at an intermediate state.For example, a mechanism such as reversing spring can be added. Such avariable optical attenuator 100 can be considered as a special variableoptical attenuator 100 in which the light attenuation is set to bebinary, and can be used as the on/off switch.

FIG. 54 shows a variable optical attenuator 101 in which two opticalfibers for output are provided parallel and, which can be used as avariable splitter. That is, two optical fibers for output 13 a, 13 b areheld parallel to each other at an output side of the fiber array 14, andinjection lenses 24 are provided opposing to end faces of both theoptical fibers for output 13 a, 13 b respectively. Thus, when the mirrormember 17 is located at a position in FIG. 54( a), 100% of the lightemitted from the optical fiber for input 12 is injected into the opticalfiber for output 13 a; when the mirror member 17 is located at aposition in FIG. 54( b), the light emitted from the optical fiber forinput 12 is injected into the optical fiber for output 13 a and theoptical fiber for output 13 b in a ratio according to a position of themirror member 17; and when the mirror member 17 is located at a positionin FIG. 54( c), 100% of the light emitted from the optical fiber forinput 12 is injected into the optical fiber for output 13 b. Therefore,the variable optical attenuator 101 can optionally change a divisionratio between the optical fiber for output 13 a and the optical fiberfor output 13 b by sliding the mirror member 17, and can be used as thevariable splitter.

FIGS. 55( a), (b) and (c) are schematic views for illustrating a methodfor producing the hybrid lens 35. It is a so-called 2P(Photo-Polymerization) method, wherein ultraviolet curing resin is usedto mold the lens. First, as shown in FIG. 55( a), a certain quantity ofultraviolet curing resin 103 is dropped on a glass substrate 102 using asyringe and the like. Then, a stumper 104 is laid on the glass substrate102 from a top of the ultraviolet curing resin 103. A concave mold 105having an inversion pattern of the hybrid lens 35 has been previouslyprovided on a lower surface of the stumper 104. Then, the stumper 104 ispressed against the glass substrate 102, thereby the ultraviolet curingresin 103 is spread out in the concave mold 105 in the stumper 104.Then, as shown in FIG. 55( b), the ultraviolet curing resin 103 isirradiated with ultraviolet rays through the glass substrate 102, andthe hybrid lens 35 is molded by curing the ultraviolet curing resin 103.When the stumper 104 is peeled from the glass substrate 102, the hybridlens 35 as a whole is integrally molded by the ultraviolet curing resin103 on an upper surface of the glass substrate 102. Although onlymolding of the hybrid lens 35 is described here, the emission lens 23and the injection lens 24 are similarly molded together with the hybridlens 35. Accordingly, the lens array 22 is produced.

To produce the stumper 104, an original mold having the same pattern asthe hybrid lens 35 is produced by, for example, laser processing, andthen an inversion mold is produced by depositing Ni and the like on theoriginal mold by an electroforming method and the like. The same concavemold pattern as the concave mold 105 in the stumper 104 is formed in theinversion mold peeled from the original mold. Then, duplication of theoriginal mold is produced from the inversion mold, and the stumper 104is produced from the duplication.

Numerical values written in the description of the embodiments aremerely an example, and the invention is not intended to be limited tothe above numerical values. In addition, while the optical fiber is usedas an optical transmission channel in the embodiments, the opticalwaveguide channel can be used without problems.

According to the variable optical attenuator of the invention describedhereinbefore, the light reflection surface for reflecting the lightemitted from the optical transmission channel for input is straightlymoved by the actuator, thereby the optical axis of the light injectedinto the optical transmission channel for output can be moved relativelyto the optical transmission channel for output, and thereby the lightattenuation can be varied. Therefore, since it has a simple structurethat the light reflection surface for reflecting the light emitted fromthe optical transmission channel for input is only straightly moved bythe actuator, the variable optical attenuator can be miniaturized. Inaddition, because of only straightly moving the light reflectionsurface, the light attenuation does not sensitively respond to variationduring moving the light reflection surface, and the light attenuationcan be accurately controlled.

Accordingly, according to the invention, the light attenuation can becontrolled in a simple structure, therefore the variable opticalattenuator can be produced at low price.

INDUSTRIAL APPLICABILITY

The invention can be used for an application such as relativelyshort-distance optical-transmission or transmission of data or signalsthrough optical fibers which connects the household devices to eachtogether.

1. A variable optical attenuator able to adjust optical attenuation,comprising: a first optical transmission channel; a second opticaltransmission channel; at least one light reflection surface; and anactuator, wherein the at least one light reflection surface reflectslight emitted from the first optical transmission channel into thesecond transmission channel, and the actuator moves an entirety of theat least one light reflection surface linearly along a directionorthogonal to a light axis of the light emitted from the first opticaltransmission channel, relative to at least one of the first opticaltransmission channel and the second optical transmission channel.
 2. Thevariable optical attenuator according to claim 1, wherein the actuatorcomprises a voice coil motor and a latch mechanism.
 3. The variableoptical attenuator according to claim 1, further comprising a fiberarray that holds the first optical transmission channel and the secondoptical transmission channel arranged parallel to each other.
 4. Thevariable optical attenuator according to claim 1, wherein the at leastone light reflection surface is formed from a boundary face betweentransparent media having different refractive indicia and perfectlyreflects light.
 5. A variable optical attenuator that attenuates lightinjected from an optical transmission channel for input and outputs thelight into an optical transmission channel for output and that canadjust optical attenuation, wherein the optical transmission channel forinput, the optical transmission channel for output, light reflectionsurfaces that reflect light emitted from the optical transmissionchannel for input to the optical transmission channel for output, and anactuator that moves all or part of the light reflection surfacesrelatively and straightly to at least one of the optical transmissionchannel for input or the optical transmission channel for output, andthe actuator moves straightly one of at least part of the lightreflection surfaces, and any one of the optical transmission channel forinput and the optical transmission channel for output such that anoptical axis of the light reflected to the optical transmission channelfor emission is displaced with respect to an axis center of the opticaltransmission channel for emission.
 6. A variable optical attenuator thatattenuates light injected from an optical transmission channel for inputand outputs the light into an optical transmission channel for outputand that can adjust optical attenuation, wherein the opticaltransmission channel for input, the optical transmission channel foroutput, light reflection surfaces that reflect light emitted from theoptical transmission channel for input to the optical transmissionchannel for output, and an actuator that moves all or part of the lightreflection surfaces relatively and straightly to at least one of theoptical transmission channel for input or the optical transmissionchannel for output, and further comprising: a monitor part that receiveslight which is emitted from the transmission channel for input but notinjected into the optical transmission channel for output.
 7. Thevariable optical attenuator according to claim 6, wherein an injectionlens disposed oppositely to a light injection surface of the opticaltransmission channel for output and a monitor lens disposed oppositelyto a light injection surface of the monitor part are unified.
 8. Thevariable optical attenuator according to claim 6, which has a functionof correcting a position of the light reflection surfaces depending onoutput from the monitor part.
 9. A variable optical attenuator thatattenuates light injected from an optical transmission channel for inputand outputs the light into an optical transmission channel for outputand that can adjust optical attenuation, wherein the opticaltransmission channel for input, the optical transmission channel foroutput, light reflection surfaces that reflect light emitted from theoptical transmission channel for input to the optical transmissionchannel for output, and an actuator that moves all or part of the lightreflection surfaces relatively and straightly to at least one of theoptical transmission channel for input or the optical transmissionchannel for output, and further comprising: a mirror member having thelight reflection surfaces that are two surfaces making an angle of 90degrees, and the actuator that straightly moves the mirror member.